Quantum dots and devices including the same

ABSTRACT

A quantum dot including: a core including a first semiconductor nanocrystal material including zinc, tellurium, and selenium; and a semiconductor nanocrystal shell disposed on the core, the semiconductor nanocrystal shell including zinc, selenium, and sulfur, wherein the quantum dot does not include cadmium, and in the quantum dot, a mole ratio of the sulfur with respect to the selenium is less than or equal to about 2.4:1. A production method of the quantum dot and an electronic device including the same are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of application Ser. No.16/298,108, filed Mar. 11, 2019, which claims priority to and thebenefit of Korean Patent Application No. 10-2018-0028321 filed in theKorean Intellectual Property Office on Mar. 9, 2018, and all thebenefits accruing therefrom under 35 U.S.C. § 119, the entire content ofwhich is incorporated herein by reference.

BACKGROUND 1. Field

A quantum dot and a device including the same are disclosed.

2. Description of the Related Art

Unlike bulk materials, physical characteristics (e.g., energy bandgapsand melting points) of nanoparticles may be controlled by changing thenanoparticle sizes. For example, a semiconductor nanocrystal particle(also known as a quantum dot) is a crystalline material having a size ofseveral nanometers. The semiconductor nanocrystal particle has arelatively small size and a large surface area per unit volume andexhibits a quantum confinement effect, and thus may have differentproperties than bulk materials having the same composition. A quantumdot may absorb light from an excitation source to be excited, and mayemit energy corresponding to an energy bandgap of the quantum dot.

Quantum dots may be synthesized using a vapor deposition method such asmetal organic chemical vapor deposition (MOCVD), molecular beam epitaxy(MBE), or the like, a wet chemical method including adding precursormaterials to an organic solvent to grow crystals, or the like. In thewet chemical method, organic compounds such as ligands/coordinatingsolvents may be coordinated on, e.g., bound to, surfaces of nanocrystalsto control crystal growth.

In order to improve photoluminescence properties of quantum dots, acore-shell structure may be used, but core-shell quantum dots havingimproved properties may be cadmium-based materials. Accordingly, thereremains a need for development of cadmium-free semiconductor nanocrystalparticles having desirable photoluminescence properties.

SUMMARY

An embodiment provides a cadmium-free semiconductor nanocrystal particlecapable of emitting blue light with improved efficiency.

An embodiment provides a method of manufacturing the semiconductornanocrystal particle.

An embodiment provides an electronic device including the semiconductornanocrystal particle.

In an embodiment, a quantum dot includes a core including a firstsemiconductor nanocrystal material including zinc, tellurium, andselenium; and a semiconductor nanocrystal shell disposed on at least aportion of the core, the semiconductor nanocrystal shell including asecond semiconductor nanocrystal material comprising zinc, selenium, andsulfur, wherein the quantum dot does not include cadmium, and a moleratio of sulfur with respect to selenium is less than or equal to about2.4:1.

A maximum photoluminescent peak wavelength of the quantum dot may begreater than or equal to about 430 nanometers (nm) and less than orequal to about 480 nm.

The quantum dot may have a size of greater than or equal to about 10 nm.

In the quantum dot, a mole ratio of tellurium with respect to seleniummay be less than or equal to about 0.05:1.

In the quantum dot, the mole ratio of sulfur with respect to seleniummay be less than or equal to about 2:1.

In the quantum dot, the mole ratio of sulfur with respect to seleniummay be less than or equal to about 1.85:1.

In the quantum dot, the mole ratio of sulfur with respect to seleniummay be less than about 1.85:1.

In the quantum dot, the mole ratio of sulfur with respect to seleniummay be less than or equal to about 1.8:1.

A size of the core may be greater than or equal to about 2 nm.

The core may include ZnTe_(x)Se_(1-x), wherein x is greater than 0 andless than or equal to about 0.05.

The semiconductor nanocrystal shell may have a gradient compositionvarying in a radial direction from the core toward an outermost surfaceof the quantum dot.

In the semiconductor nanocrystal shell, an amount of the sulfur mayincrease in a radial direction from the core toward an outermost surfaceof the quantum dot.

The semiconductor nanocrystal shell may include a first layer disposeddirectly on the core and a second layer disposed on the first layer. Thefirst layer may include a second semiconductor nanocrystal. The secondlayer may include a third semiconductor nanocrystal having a compositiondifferent from a composition of the second semiconductor nanocrystal.

The second semiconductor nanocrystal may include zinc, selenium, andsulfur. The third semiconductor nanocrystal may include zinc and sulfur.

The second layer may be an outermost layer and the third semiconductornanocrystal may not include selenium.

A maximum photoluminescent peak wavelength of the quantum dot may begreater than or equal to about 445 nm.

A maximum photoluminescent peak wavelength of the quantum dot may beless than or equal to about 470 nm.

The quantum dot may have quantum efficiency of greater than or equal toabout 70%.

A full width at half maximum (FWHM) of a maximum photoluminescent peakof the quantum dot may be less than about 30 nm.

The quantum dot may have a size of greater than or equal to about 12 nm.

In an embodiment, an electroluminescent device includes a firstelectrode and a second electrode facing each other, and a light emittinglayer disposed between the first electrode and the second electrode, thelight emitting layer including a quantum dot (e.g., a plurality ofquantum dots), wherein the quantum dot includes the aforementionedquantum dot.

The electroluminescent device may further include a charge auxiliarylayer between the first electrode and the light emitting layer, betweenthe second electrode and the light emitting layer, or between the firstelectrode and the light emitting layer and between the second electrodeand the light emitting layer.

The charge auxiliary layer may include a charge injection layer, acharge transport layer, or a combination thereof.

A peak external quantum efficiency of the electroluminescent device maybe greater than or equal to about 4%.

The electroluminescent device may emit light having an x value of a CIEcolor space chromaticity diagram that is less than or equal to about0.2.

In an embodiment, an electronic device includes the aforementionedquantum dot.

The electronic device may be a display device, a light emitting diode(LED), a quantum dot light emitting diode (QLED), an organic lightemitting diode (OLED), a sensor, an image sensor, or a solar cell.

A cadmium-free quantum dot capable of emitting blue light may beprovided. The quantum dot may be applied to, e.g., used in, variousdisplay devices, biolabeling (biosensor, bioimaging), a photodetector, asolar cell, a hybrid composite, or the like. The quantum dots of anembodiment may exhibit improved External Quantum Efficiency (EQE) andincreased Maximum brightness when they are applied, e.g., used, in anelectroluminescent device. The quantum dots of an embodiment may exhibitdecreased FWHM and increased quantum efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages and features of this disclosure willbecome more apparent by describing in further detail exemplaryembodiments thereof with reference to the accompanying drawings, inwhich:

FIG. 1 is a schematic cross-sectional view of a semiconductornanocrystal according to an embodiment.

FIG. 2 is a schematic cross-sectional view of a quantum dot (QD) LEDdevice according to an embodiment.

FIG. 3 is a schematic cross-sectional view of a QD LED device accordingto an embodiment.

FIG. 4 is a schematic cross-sectional view of a QD LED device accordingto an embodiment.

DETAILED DESCRIPTION

Advantages and characteristics of this disclosure, and a method forachieving the same, will become evident referring to the followingexample embodiments together with the drawings attached hereto. However,the embodiments should not be construed as being limited to theembodiments set forth herein. Unless otherwise defined, all terms usedin the specification (including technical and scientific terms) may beused with meanings commonly understood by a person having ordinaryknowledge in the art. The terms defined in a generally-used dictionarymay not be interpreted ideally or exaggeratedly unless clearly defined.In addition, unless explicitly described to the contrary, the word“comprise” and variations such as “comprises” or “comprising”, will beunderstood to imply the inclusion of stated elements but not theexclusion of any other elements.

Further, the singular includes the plural unless mentioned otherwise.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity. Like reference numerals designate likeelements throughout the specification.

It will be understood that when an element such as a layer, film,region, or substrate is referred to as being “on” another element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” another element, there are no intervening elements present.

It will be understood that, although the terms “first,” “second,”“third” etc. may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are only used to distinguish one element, component, region,layer or section from another element, component, region, layer orsection. Thus, “a first element,” “component,” “region,” “layer” or“section” discussed below could be termed a second element, component,region, layer or section without departing from the teachings herein.

“About” as used herein is inclusive of the stated value and means withinan acceptable range of deviation for the particular value as determinedby one of ordinary skill in the art, considering the measurement inquestion and the error associated with measurement of the particularquantity (i.e., the limitations of the measurement system). For example,“about” can mean within one or more standard deviations, or within ±10%or 5% of the stated value.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

As used herein, when a definition is not otherwise provided,“substituted” refers to a compound or a moiety, wherein at least one ofhydrogen atoms thereof is replaced by a substituent, wherein thesubstituent may be a C1 to C30 alkyl group, a C2 to C30 alkenyl group, aC2 to C30 alkynyl group, a C6 to C30 aryl group, a C7 to C30 alkylarylgroup, a C1 to C30 alkoxy group, a C1 to C30 heteroalkyl group, a C3 toC30 heteroalkylaryl group, a C3 to C30 cycloalkyl group, a C3 to C15cycloalkenyl group, a C6 to C30 cycloalkynyl group, a C2 to C30heterocycloalkyl group, a halogen (—F, —Cl, —Br, or —I), a hydroxy group(—OH), a nitro group (—NO₂), a cyano group (—CN), an amino group (—NRR′wherein R and R′ are independently hydrogen or a C1 to C6 alkyl group),an azido group (—N₃), an amidino group (—C(═NH)NH₂)), a hydrazino group(—NHNH₂), a hydrazono group (═N(NH₂)), an aldehyde group (—C(═O)H), acarbamoyl group (—C(O)NH₂), a thiol group (—SH), an ester group(—C(═O)OR, wherein R is a 01 to C6 alkyl group or a C6 to C12 arylgroup), a carboxyl group (—COOH) or a salt thereof (—C(═O)OM, wherein Mis an organic or inorganic cation), a sulfonic acid group (—SO₃H) or asalt thereof (—SO₃M, wherein M is an organic or inorganic cation), aphosphoric acid group (—PO₃H₂) or a salt thereof (—PO₃MH or —PO₃M₂,wherein M is an organic or inorganic cation), or a combination thereof.

As used herein, a hydrocarbon group refers to a group including carbonand hydrogen (e.g., an alkyl, alkenyl, alkynyl, or aryl group). Thehydrocarbon group may be a group having a monovalence or greater formedby removal of one or more hydrogen atoms from, alkane, alkene, alkyne,or arene. In the hydrocarbon group, at least one methylene may bereplaced by an oxide moiety, a carbonyl moiety, an ester moiety, —NH—,or a combination thereof.

Herein, “aliphatic” refers to a saturated or unsaturated linear orbranched hydrocarbon group. An aliphatic group may be an alkyl, alkenyl,or alkynyl group, for example.

As used herein, “alkyl” refers to a linear or branched saturatedmonovalent hydrocarbon group (methyl, ethyl, hexyl, etc.).

As used herein, “alkenyl” refers to a linear or branched monovalenthydrocarbon group having one or more carbon-carbon double bond.

As used herein, “alkynyl” refers to a linear or branched monovalenthydrocarbon group having one or more carbon-carbon triple bond.

Herein, “aromatic” refers to an organic compound or group comprising atleast one unsaturated cyclic group having delocalized pi electrons. Theterm encompasses both hydrocarbon aromatic compounds and heteroaromaticcompounds.

As used herein, “aryl” refers to a group formed by removal of at leastone hydrogen from an aromatic hydrocarbon (e.g., a phenyl or naphthylgroup).

As used herein, “hetero” refers to one including one or more (e.g., 1 to3) heteroatom of N, O, S, Si, P, or a combination thereof.

As used herein, “Group” refers to a group of Periodic Table.

As used herein, the phrases “External Quantum Efficiency”, “QuantumEfficiency”, and “Quantum Yield” are interchangeable.

A core-shell structure may improve photoluminescence properties ofquantum dots, but core-shell quantum dots having desirable propertiesmay include cadmium. Provided are cadmium-free semiconductor nanocrystalparticles having desirable photoluminescence properties.

Semiconductor nanocrystal particles (hereinafter, also referred to as aquantum dots) may absorb light from an excitation source and may emitlight corresponding to an energy bandgap of the semiconductornanocrystal particles. The energy bandgap of the quantum dot may bechanged depending on a size and a composition of the quantum dot. Forexample, as the size of the quantum dot increases, the quantum dot mayhave a narrower energy bandgap and may exhibit an increased lightemitting wavelength. Semiconductor nanocrystals may be used as a lightemitting material in various fields such as a display device, an energydevice, or a bio light emitting device.

Quantum dots having relatively increased photoluminescence propertiesmay include cadmium (Cd). The cadmium may raise environmental and/orhealth issues and is a restricted element defined under Restriction ofHazardous Substances Directive (RoHS) in a plurality of countries.Accordingly, there remain a need for development of a cadmium-freequantum dot having improved photoluminescence characteristics. In orderto be applied to, e.g., used in, a QLED display device, a quantum dothaving a relatively narrow full width at half maximum (FWHM) and capableof emitting light of pure blue (e.g., PL peak around 455 nm) is desired.For example, a blue light emitting material is desired for a displaydevice having a relatively high (e.g., about 90% or greater) colorreproducibility under a next generation color standard such as BT2020. Acadmium-free quantum dot having desirable photoluminescence propertiesand PL peak within the foregoing ranges is provided.

A quantum dot according to an embodiment has a structure and acomposition that will be described herein, and thereby may not includecadmium and may emit blue light.

The quantum dot includes a core including a first semiconductornanocrystal material including zinc, tellurium, and selenium; and asemiconductor nanocrystal shell disposed on (at least a portion of) thecore and including a second semiconductor nanocrystal material differentfrom the first semiconductor nanocrystal material (and including zinc,selenium, and sulfur). The quantum dot does not include cadmium. In thequantum dot, a mole ratio of sulfur with respect to the selenium is lessthan or equal to about 2.4:1. The quantum dot may emit (blue) lighthaving a maximum photoluminescent peak wavelength in a range of greaterthan or equal to about 430 nanometers (nm) and less than or equal toabout 480 nm.

The first semiconductor nanocrystal material of the core may include alimited amount of tellurium (Te). The core may include ZnTe_(x)Se_(1-x),wherein x is greater than about 0 and less than or equal to about 0.05.In the core, the wavelength of the maximum light emitting peak of thequantum dot may be increased by increasing a ratio of an amount oftellurium relative to an amount of selenium. In the core, the amount ofthe tellurium may be greater than or equal to about 0.001 moles, greaterthan or equal to about 0.005 moles, greater than or equal to about 0.006moles, greater than or equal to about 0.007 moles, greater than or equalto about 0.008 moles, greater than or equal to about 0.009 moles,greater than or equal to about 0.01 moles, or greater than or equal toabout 0.02:1 moles based on one mole of the selenium. In the core, theamount of the tellurium with respect to one mole of the selenium may beless than or equal to about 0.053 moles, for example, less than or equalto about 0.05 moles, less than or equal to about 0.049 moles, less thanor equal to about 0.048 moles, less than or equal to about 0.047 moles,less than or equal to about 0.046 moles, less than or equal to about0.045 moles, less than or equal to about 0.044 moles, less than or equalto about 0.043 moles, less than or equal to about 0.042 moles, less thanor equal to about 0.041 moles, or less than or equal to about 0.04moles.

The core or the quantum dot may not include manganese, copper, or acombination thereof.

In an embodiment, the semiconductor nanocrystal shell includes zinc(Zn), selenium (Se), and sulfur (S). The shell may be a multi-layeredshell including a plurality of layers. In the plurality of layers forthe shell, adjacent layers may have semiconductor nanocrystal materialof different compositions. The multi-layered shell may include a firstlayer disposed directly on the core and a second layer disposed on orover the first layer. The first layer may include a second semiconductornanocrystal. The second layer may include a third semiconductornanocrystal having a composition different from the second semiconductornanocrystal. The second layer may be the outermost layer of the quantumdot (see FIG. 1). The second semiconductor nanocrystal may include zinc,selenium, and optionally sulfur. The third semiconductor nanocrystal mayinclude zinc and sulfur. The third semiconductor nanocrystal may notinclude selenium. In FIG. 1, a cross-section of the quantum dot isillustrated as a circle, but it is not limited thereto. Thecross-section of the quantum dot may have any suitable shape.

In the shell or the multi-layered shell, each of the layer may include agradient alloy having a composition varying in a direction of a radius,e.g., a radial direction from the core toward an outermost surface ofthe quantum dot. In an embodiment, an amount of the sulfur in thesemiconductor nanocrystal shell may increase toward a surface of thequantum dot. For example, in the shell, the amount of the sulfur mayincrease in a direction away from the core, e.g., in a radial directionfrom the core toward an outermost surface of the quantum dot.

The quantum dot may have a mole ratio of tellurium relative to selenium(e.g., measured by inductively coupled plasma-atomic emissionspectroscopy (ICP-AES)) of less than or equal to about 0.05:1, less thanor equal to about 0.04:1, less than or equal to about 0.03:1, less thanor equal to about 0.02:1, or less than or equal to about 0.01:1. Themole ratio of the tellurium to the selenium may be greater than or equalto about 0.001:1, greater than or equal to about 0.0015:1, greater thanor equal to about 0.002:1, greater than or equal to about 0.0025:1,greater than or equal to about 0.003:1, greater than or equal to about0.0035:1, greater than or equal to about 0.004:1, or greater than orequal to about 0.0045:1. The mole ratio of the tellurium to the seleniummay be about 0.004:1 to about 0.01:1. The mole ratio of the tellurium tothe selenium may be about 0.001:1 to about 0.02:1. The mole ratio of thetellurium to the selenium may be about 0.001:1 to about 0.03:1.

In the quantum dot, a mole ratio of the tellurium with respect to thezinc (e.g., determined by an inductively coupled plasma-atomic emissionspectroscopy) may be less than or equal to about 0.02:1, less than orequal to about 0.019:1, less than or equal to about 0.018:1, less thanor equal to about 0.017:1, less than or equal to about 0.016:1, lessthan or equal to about 0.015:1, less than or equal to about 0.014:1,less than or equal to about 0.013:1, less than or equal to about0.012:1, less than or equal to about 0.011:1, less than or equal toabout 0.010:1, less than or equal to about 0.009:1, less than or equalto about 0.008:1, less than or equal to about 0.007:1, less than orequal to about 0.006:1, or less than or equal to about 0.005:1. A moleratio of the tellurium with respect to the zinc may be greater than orequal to about 0.001:1, for example, greater than or equal to about0.0015:1

An amount of zinc (Zn) may be greater than that of selenium (Se). Anamount of zinc (Zn) may be greater than that of selenium (Se) and anamount of selenium may be greater than that of tellurium, for example,as measured by an ICP-AES analysis of the semiconductor nanocrystalparticle.

For example, in the ICP-AES analysis, a mole ratio of Se to Zn may beless than about 1:1, for example, less than or equal to about 0.95:1,less than or equal to about 0.90:1, less than or equal to about 0.85:1,less than or equal to about 0.8:1, less than or equal to about 0.7:1,less than or equal to about 0.6:1, less than or equal to about 0.5:1, orless than or equal to about 0.45:1. In an embodiment, (for example, inthe ICP-AES analysis) a mole ratio of Se to Zn may be greater than orequal to about 0.1:1, for example, greater than or equal to about 0.2:1,or greater than or equal to about 0.3:1.

In the quantum dot, a mole ratio of sulfur to Zn may be greater than orequal to about 0.1:1, for example, greater than or equal to about0.15:1, greater than or equal to about 0.2:1, or greater than or equalto about 0.3:1, greater than or equal to about 0.4:1. In the quantumdot, the mole ratio of sulfur to Zn may be less than or equal to about0.9:1, for example, less than or equal to about 0.8:1, less than orequal to about 0.7:1, or less than or equal to about 0.6:1.

In the quantum dot, a mole ratio of Se+S to zinc ((Se+S):Zn) may begreater than or equal to about 0.3:1, greater than or equal to about0.4:1, greater than or equal to about 0.5:1, greater than or equal toabout 0.6:1, greater than or equal to about 0.7:1, greater than or equalto about 0.8:1, greater than or equal to about 0.85:1, or greater thanor equal to about 0.89:1. In the semiconductor nanocrystal particle, amole ratio of Se and S to zinc may be less than or equal to about 1:1.

In the quantum dot, a mole ratio of sulfur with respect to selenium isless than or equal to about 2.4:1. In the quantum dot, a mole ratio ofsulfur with respect to selenium may be less than or equal to about 2:1,less than or equal to about 1.95:1, less than or equal to about 1.9:1,less than or equal to about 1.85:1, less than or equal to about 1.80:1,less than or equal to about 1.40:1, less than or equal to about 1.25:1,less than or equal to about 1.19:1, less than or equal to about 0.95:1,or less than or equal to about 0.80:1. In a quantum dot of anembodiment, a mole ratio of sulfur with respect to selenium may begreater than or equal to about 0.4:1, greater than or equal to about0.5:1, greater than or equal to about 0.6:1, greater than or equal toabout 0.7:1, greater than or equal to about 0.95:1, greater than orequal to about 1:1, greater than or equal to about 1.1:1, greater thanor equal to about 1.23:1, greater than or equal to about 1.25:1, greaterthan or equal to about 1.3:1, greater than or equal to about 1.4:1, orgreater than or equal to about 1.95:1.

With the aforementioned ratios between the components, the quantum dotof an embodiment may emit blue light with improved quantum efficiency(e.g., of greater than or equal to about 70%, for example, greater thanor equal to about 71%, greater than or equal to about 72%, greater thanor equal to about 73%, greater than or equal to about 74%, or greaterthan or equal to about 75%) and a decreased FWHM (e.g., of less thanabout 30 nm, less than or equal to about 25 nm, or less than or equal toabout 22 nm). The quantum dot may have a quantum efficiency of greaterthan or equal to about 80%, greater than or equal to about 90%, greaterthan or equal to about 95%, greater than or equal to about 99%, or 100%.

The quantum dot may include various shapes. The shape of the quantum dotmay include a spherical shape, a polygonal shape, a multipod shape, or acombination thereof. In an embodiment, the quantum dot may have amultipod shape. The multipod may have at least two (e.g., at least threeor at least four) branch parts and a valley part therebetween.

A size of the core may be greater than or equal to about 2 nm, forexample, greater than or equal to about 3 nm or greater than or equal toabout 4 nm. A size of the core may be less than or equal to about 6 nm,for example, less than or equal to about 5 nm. The quantum dot may havea relatively large size and may emit blue light, and thus may haveenhanced stability and be handled relatively easily. In an embodiment,the quantum dot may have a size of greater than or equal to about 10 nm,for example, greater than or equal to about 11 nm, or even greater thanor equal to about 12 nm. In an embodiment, a size of the quantum dot mayrefer to a diameter. In a case in which the quantum dot is non-sphericalshape, a size of the quantum dot may refer to a diameter calculated froma two-dimensional image obtained from an electron microscopic analysis(e.g., under an assumption that the image is a circle). The size of thequantum dot may be less than or equal to about 50 nm, for example, lessthan or equal to about 45 nm, less than or equal to about 40 nm, lessthan or equal to about 35 nm, less than or equal to about 30 nm, lessthan or equal to about 25 nm, less than or equal to about 24 nm, lessthan or equal to about 23 nm, less than or equal to about 22 nm, lessthan or equal to about 21 nm, less than or equal to about 20 nm, lessthan or equal to about 19 nm, less than or equal to about 18 nm, lessthan or equal to about 17 nm, or less than or equal to about 16 nm.

A quantum dot of an embodiment may emit blue light having a maximum peakemission at a wavelength of greater than or equal to about 430 nm, e.g.,greater than or equal to about 440 nm, greater than or equal to about445 nm, greater than or equal to about 447 nm, greater than or equal toabout 448 nm, greater than or equal to about 449 nm, or greater than orequal to about 450 nm, and less than or equal to about 480 nm, e.g.,less than or equal to about 475 nm, less than or equal to about 470 nm,less than or equal to about 465 nm, less than or equal to about 460 nm,or less than or equal to about 455 nm. The blue light may have a maximumlight-emitting peak wavelength of from about 450 nm to about 460 nm.

The maximum peak emission may have a full width at half maximum (FWHM)of less than or equal to about 50 nm, for example, less than or equal toabout 49 nm, less than or equal to about 48 nm, less than or equal toabout 47 nm, less than or equal to about 46 nm, less than or equal toabout 45 nm, less than or equal to about 44 nm, less than or equal toabout 43 nm, less than or equal to about 42 nm, less than or equal toabout 41 nm, less than or equal to about 40 nm, less than or equal toabout 39 nm, less than or equal to about 38 nm, less than or equal toabout 37 nm, less than or equal to about 36 nm, less than or equal toabout 35 nm, less than or equal to about 34 nm, less than or equal toabout 33 nm, less than or equal to about 32 nm, less than or equal toabout 31 nm, less than or equal to about 30 nm, less than or equal toabout 29 nm, or less than or equal to about 28 nm.

Cadmium free quantum dots may not emit blue light of a desiredwavelength (for example, greater than or equal to about 430 nm and lessthan or equal to about 470 nm) with enhanced efficiency and a narrowFWHM. For example, an indium phosphide quantum dot has a relatively lowefficiency and it may not be possible to control an emission wavelengthof a ZnSe quantum dot to be greater than about 430 nm. The quantum dotof an embodiment may emit blue light with improved efficiency and anarrow FWHM. In addition, the quantum dot of an embodiment may exhibitincreased maximum EQE in an electroluminescent device.

In an embodiment, a method of producing the quantum dot includespreparing a core including a first semiconductor nanocrystal includingzinc, selenium, and tellurium (hereinafter, also referred to as a core);and

reacting a zinc precursor, and a selenium precursor, a sulfur precursor,or a combination thereof a plurality of times in the presence of thecore and an organic ligand in an organic solvent to form a semiconductornanocrystal shell including zinc, selenium, and sulfur and having theaforementioned composition on a surface of the core.

The formation of the semiconductor nanocrystal shell may includereacting the zinc precursor and the selenium precursor, and thenreacting the zinc precursor and the sulfur precursor.

In an embodiment, the core may be obtained by preparing a zinc precursorsolution including a zinc precursor and an organic ligand; preparing aselenium precursor and a tellurium precursor; heating the zinc precursorsolution to a first reaction temperature and adding the seleniumprecursor and the tellurium precursor thereto optionally together withan organic ligand to proceed a reaction therebetween.

The zinc precursor may include a Zn powder, ZnO, an alkylated Zncompound (e.g., C2 to C30 dialkyl zinc such as diethyl zinc), a Znalkoxide (e.g., a zinc ethoxide), a Zn carboxylate (e.g., a zincacetate), a Zn nitrate, a Zn perchlorate, a Zn sulfate, a Znacetylacetonate, a Zn halide (e.g., a zinc chloride), a Zn cyanide, a Znhydroxide, zinc carbonate, zinc peroxide, or a combination thereof.Examples of the zinc precursor may include dimethyl zinc, diethyl zinc,zinc acetate, zinc acetylacetonate, zinc iodide, zinc bromide, zincchloride, zinc fluoride, zinc carbonate, zinc cyanide, zinc nitrate,zinc oxide, zinc peroxide, zinc perchlorate, zinc sulfate, or acombination thereof.

The selenium precursor may include selenium-trioctylphosphine (Se-TOP),selenium-tributylphosphine (Se-TBP), selenium-triphenylphosphine(Se-TPP), selenium-diphenylphosphine (Se-DPP), or a combination thereof,but is not limited thereto.

The tellurium precursor may include tellurium-trioctylphosphine(Te-TOP), tellurium-tributylphosphine (Te-TBP),tellurium-triphenylphosphine (Te-TPP), or a combination thereof, but isnot limited thereto.

The sulfur precursor may include hexane thiol, octane thiol, decanethiol, dodecane thiol, hexadecane thiol, mercapto propyl silane,sulfur-trioctylphosphine (S-TOP), sulfur-tributylphosphine (S-TBP),sulfur-triphenylphosphine (S-TPP), sulfur-trioctylamine (S-TOA),bistrimethylsilyl sulfur, ammonium sulfide, sodium sulfide, or acombination thereof.

The organic solvent may be a C6 to C22 primary amine such as ahexadecylamine, a C6 to C22 secondary amine such as dioctylamine, a C6to C40 tertiary amine such as a trioctyl amine, a nitrogen-containingheterocyclic compound such as pyridine, a C6 to C40 olefin such asoctadecene, a C6 to C40 aliphatic hydrocarbon group such as hexadecane,octadecane, or squalane, an aromatic hydrocarbon group substituted witha C6 to C30 alkyl group such as phenyldodecane, phenyltetradecane, orphenyl hexadecane, a primary, secondary, or tertiary phosphine (e.g.,trioctyl phosphine) substituted with at least one (e.g., 1, 2, or 3) C6to C22 alkyl group, a primary, secondary, or tertiary phosphine oxide(e.g., trioctylphosphine oxide) substituted with a (e.g., 1, 2, or 3) C6to C22 alkyl group(s), a C12 to C22 aromatic ether such as a phenylether or a benzyl ether, or a combination thereof.

The organic ligand may coordinate, e.g., be bound to, the surface of theproduced nanocrystal and may have an effect on the light emitting andelectric characteristics as well as may effectively disperse thenanocrystal in the solution phase. The organic ligand may include RCOOH,RNH₂, R₂NH, R₃N, RSH, RH₂PO, R₂HPO, R₃PO, RH₂P, R₂HP, R₃P, ROH, RCOOR,RPO(OH)₂, R₂POOH, wherein R is the same or different and is eachindependently hydrogen, a substituted or unsubstituted C1 to C24 (or C3to C40) aliphatic hydrocarbon group, a substituted or unsubstituted C6to C20 (or C6 to C40) aromatic hydrocarbon group, or a combinationthereof provided that at least one of the R is not hydrogen, or acombination thereof. One or more ligands may be may be used.

Examples of the organic ligand compound may include methane thiol,ethane thiol, propane thiol, butane thiol, pentane thiol, hexane thiol,octane thiol, dodecane thiol, hexadecane thiol, octadecane thiol, benzylthiol; methane amine, ethane amine, propane amine, butane amine, pentaneamine, hexane amine, octane amine, dodecane amine, hexadecyl amine,oleyl amine, octadecyl amine, dimethyl amine, diethyl amine, dipropylamine; methanoic acid, ethanoic acid, propanoic acid, butanoic acid,pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, dodecanoicacid, hexadecanoic acid, octadecanoic acid, oleic acid, benzoic acid,palmitic acid, stearic acid; a phosphine such as methyl phosphine, ethylphosphine, propyl phosphine, butyl phosphine, pentyl phosphine,tributylphosphine, or trioctylphosphine; a phosphine oxide such asmethyl phosphine oxide, ethyl phosphine oxide, propyl phosphine oxide,butyl phosphine oxide, or trioctylphosphine oxide; a diphenyl phosphineor triphenyl phosphine compound, or an oxide compound thereof;phosphonic acid, or the like, but are not limited thereto. One or moreorganic ligand compounds may be used. In an embodiment, the organicligand compound may be a combination of RCOOH and amine, e.g., RNH₂,R₂NH, and/or R₃N, wherein R is as defined above.

In the core including the first semiconductor nanocrystal, a mole ratioof tellurium with respect to selenium may be less than or equal to about0.05:1. In order to form the core, an amount of the selenium precursorfor forming the core may be greater than or equal to about 20 moles, forexample, greater than or equal to about 25 moles, greater than or equalto about 26 moles, greater than or equal to about 27 moles, greater thanor equal to about 28 moles, greater than or equal to about 29 moles,greater than or equal to about 30 moles, greater than or equal to about31 moles, greater than or equal to about 32 moles, greater than or equalto about 33 moles, greater than or equal to about 34 moles, greater thanor equal to about 35 moles, greater than or equal to about 36 moles,greater than or equal to about 37 moles, greater than or equal to about38 moles, greater than or equal to about 39 moles, or greater than orequal to about 40 moles based on one mole of the tellurium precursor.The amount of the selenium precursor may be less than or equal to about60 moles, less than or equal to about 59 moles, less than or equal toabout 58 moles, less than or equal to about 57 moles, less than or equalto about 56 moles, or less than or equal to about 55 moles based on onemole of the tellurium precursor. Within the foregoing ranges of theamount, the core having the aforementioned composition may be formed.

The first reaction temperature may be greater than or equal to about280° C., for example, greater than or equal to about 290° C. A reactiontime for forming the core is not particularly limited and may beappropriately selected. For example, the reaction time may be greaterthan or equal to about 5 minutes, greater than or equal to about 10minutes, greater than or equal to about 15 minutes, greater than orequal to about 20 minutes, greater than or equal to about 25 minutes,greater than or equal to about 30 minutes, greater than or equal toabout 35 minutes, greater than or equal to about 40 minutes, greaterthan or equal to about 45 minutes, or greater than or equal to about 50minutes, but is not limited thereto. For example, the reaction time maybe less than or equal to about 2 hours, but is not limited thereto. Bycontrolling the reaction time, the size of the core may be controlled.

Reaction conditions for forming the shell may be selected appropriatelyin light of a desired composition of the shell. In an embodiment, asolvent and optionally an organic ligand may be heated (and/or placedunder vacuum) at a predetermined temperature (e.g., at a temperature ofgreater than or equal to about 100° C.) and an atmosphere is changedinto an inert gas and then is heated at a predetermined temperature(e.g., at a temperature of greater than or equal to about 100° C.).Then, a core may be injected, and shell precursors may be injectedsequentially or simultaneously and a resulting mixture is heated to apredetermined reaction temperature to carry out a reaction.

A mixture having different ratios of the shell precursors may besequentially added for a given period of time, e.g., a reaction time, toachieve a desired composition of the quantum dot or to form a gradientor a multi-layered shell on the core. In an embodiment, a first layermay be formed by reacting a zinc precursor and a selenium precursor andthen a second layer may be formed by reacting a zinc precursor and asulfur precursor. A reaction temperature for forming the shell may begreater than or equal to about 280° C., for example, greater than orequal to about 290° C., greater than or equal to about 300° C. and lessthan or equal to about 330° C., or less than or equal to about 325° C.

In a reaction system, an amount and a concentration of the precursor maybe selected considering the compositions of the core and the shell andthe reactivity between the precursors.

After the completion of the reaction, a non-solvent is added to reactionproducts and the nanocrystal particles coordinated with, e.g., bound to,the ligand compound may be separated. The non-solvent may be a polarsolvent that is miscible with the solvent used in the core formationand/or shell formation reactions and is not capable of dispersing theproduced nanocrystals therein. The non-solvent may be selected dependingthe solvent used in the reaction and may be, for example, acetone,ethanol, butanol, isopropanol, water, tetrahydrofuran (THF),dimethylsulfoxide (DMSO), diethylether, formaldehyde, acetaldehyde,ethylene glycol, a solvent having a similar solubility parameter to theforegoing non-solvents, or a combination thereof. Separation of thenanocrystal particles may involve centrifugation, sedimentation,chromatography, or distillation. The separated nanocrystal particles maybe added to a washing solvent and washed, if desired. The washingsolvent is not particularly limited and a solvent having similarsolubility parameter to that of the ligand may be used and examplesthereof may include hexane, heptane, octane, chloroform, toluene,benzene, or the like.

The quantum dots of the embodiment may not dispersible to water, any ofthe foregoing listed non-solvent, or a mixture thereof. The quantum dotsof the embodiment may be water-insoluble. The quantum dots of theembodiments may be dispersed the aforementioned organic solvent. In someembodiments, the quantum dots may be dispersed in a C6 to C40 aliphatichydrocarbon, a C6 to C40 aromatic hydrocarbon, or a mixture thereof.

In an embodiment, an electronic device includes the semiconductornanocrystal particle. The device may include a display device, a lightemitting diode (LED), an organic light emitting diode (OLED), a quantumdot LED, a sensor, a solar cell, an image sensor, or a liquid crystaldisplay (LCD), but is not limited thereto.

In an embodiment, the electronic device may be a photoluminescentelement (e.g., a lighting such as a quantum dot sheet or a quantum dotrail or a liquid crystal display (LCD)) or an electroluminescent device(e.g., QD LED).

In an embodiment, the electronic device may include a quantum dot sheetand the quantum dot may be included in the quantum dot sheet (e.g., in aform of a semiconductor nanocrystal-polymer composite).

In an embodiment, the electronic device may be an electroluminescentdevice. The electronic device may include an anode 1 and a cathode 5facing each other and a quantum dot emission layer 3 disposed betweenthe anode and the cathode and including a plurality of quantum dots, andthe plurality of quantum dots may include the blue light emittingsemiconductor nanocrystal particle (see FIG. 2).

The cathode may include an electron injection conductor (for example,having a relatively low work function). The anode may include a holeinjection conductor (for example, having a relatively high workfunction). The electron/hole injection conductors may include a metal(e.g., aluminum, magnesium, tungsten, nickel, cobalt, platinum,palladium, or calcium), a metal compound (e.g., LiF), an alloy, or acombination thereof; a metal oxide such as gallium indium oxide orindium tin oxide; or a conductive polymer such as polyethylenedioxythiophene (e.g., having a relatively high work function), but arenot limited thereto.

At least one of the cathode and the anode may be a light transmittingelectrode or a transparent electrode. In an embodiment, both of theanode and the cathode may be light transmitting electrodes. Theelectrode may be patterned.

The light transmitting electrode may be made of, for example, atransparent conductor such as indium tin oxide (ITO) or indium zincoxide (IZO), gallium indium tin oxide, zinc indium tin oxide, titaniumnitride, polyaniline, or LiF/Mg:Ag, or a metal thin film of a thinmonolayer or multilayer, but is not limited thereto. When one of thecathode and the anode is a non-light transmitting electrode, the cathodeor the anode may be made of, for example, an opaque conductor such asaluminum (Al), a lithium aluminum (Li:Al) alloy, a magnesium-silveralloy (Mg:Ag), or a lithium fluoride-aluminum (LiF:Al).

The light transmitting electrode may be disposed on a transparentsubstrate (e.g., insulating transparent substrate). The substrate may berigid or flexible. The substrate may be a plastic, glass, or a metal.

Thicknesses of the anode and the cathode are not particularly limitedand may be selected considering device efficiency. For example, thethickness of the anode (or the cathode) may be greater than or equal toabout 5 nm, for example, greater than or equal to about 50 nm, but isnot limited thereto. For example, the thickness of the anode (or thecathode) may be less than or equal to about 100 micrometers (μm), forexample, less than or equal to about 10 μm less than or equal to about 1μm, less than or equal to about 900 nm, less than or equal to about 500nm, or less than or equal to about 100 nm, but is not limited thereto.

The quantum dot emission layer includes a plurality of quantum dots. Theplurality of quantum dots includes the blue light emitting semiconductornanocrystal particle according to the aforementioned embodiments. Thequantum dot emission layer may include a monolayer of the blue lightemitting semiconductor nanocrystal particles.

The emissive layer may be formed by preparing a dispersion including thequantum dots dispersed in a solvent, applying the dispersion via spincoating, ink jet coating, or spray coating, and drying the same. Theemissive layer may have a thickness of greater than or equal to about 5nm, for example, greater than or equal to about 10 nm, greater than orequal to about 15 nm, greater than or equal to about 20 nm, or greaterthan or equal to about 25 nm, and less than or equal to about 100 nm,for example, less than or equal to about 90 nm, less than or equal toabout 80 nm, less than or equal to about 70 nm, less than or equal toabout 60 nm, less than or equal to about 50 nm, less than or equal toabout 40 nm, or less than or equal to about 30 nm.

The electronic device may include charge (hole or electron) auxiliarylayers between the anode and the cathode. For example, the electronicdevice may include a hole auxiliary layer 2 between the anode and thequantum dot emission layer and/or an electron auxiliary layer 4 betweenthe cathode and the quantum dot emission layer. (see FIG. 2)

In the figures, the electron/hole auxiliary layer is formed as a singlelayer, but the electron/hole auxiliary layer is not limited thereto andmay include a plurality of layers including at least two stacked layers.

The hole auxiliary layer may include, for example, a hole injectionlayer (HIL) to facilitate hole injection, a hole transport layer (HTL)to facilitate hole transport, an electron blocking layer (EBL) toinhibit electron transport, or a combination thereof. For example, thehole injection layer may be disposed between the hole transport layerand the anode. For example, the electron blocking layer may be disposedbetween the emission layer and the hole transport (injection) layer, butis not limited thereto. A thickness of each layer may be selectedappropriately. For example, a thickness of each layer may be greaterthan or equal to about 1 nm, greater than or equal to about 5 nm,greater than or equal to about 10 nm, greater than or equal to about 15nm, greater than or equal to about 20 nm, or greater than or equal toabout 25 nm, and less than or equal to about 500 nm, less than or equalto about 400 nm, less than or equal to about 300 nm, less than or equalto about 200 nm, less than or equal to about 100 nm, less than or equalto about 90 nm, less than or equal to about 80 nm, less than or equal toabout 70 nm, less than or equal to about 60 nm, less than or equal toabout 50 nm, but is not limited thereto. The hole injection layer may bean organic layer that is formed by a solution process (e.g., spincoating etc.) such as poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The hole transport layer may be an organic layerthat is formed by a solution process (e.g., spin coating, etc.).

The electron auxiliary layer may include, for example, an electroninjection layer (EIL) to facilitate electron injection, an electrontransport layer (ETL) to facilitate electron transport, a hole blockinglayer (HBL) to inhibit hole transport, or a combination thereof. Forexample, the electron injection layer may be disposed between theelectron transport layer and the cathode. For example, the hole blockinglayer may be disposed between the emission layer and the electrontransport (injection) layer, but is not limited thereto. A thickness ofeach layer may be selected appropriately. For example, a thickness ofeach layer may be greater than or equal to about 1 nm, greater than orequal to about 5 nm, greater than or equal to about 10 nm, greater thanor equal to about 15 nm, greater than or equal to about 20 nm, orgreater than or equal to about 25 nm, and less than or equal to about500 nm, less than or equal to about 400 nm, less than or equal to about300 nm, less than or equal to about 200 nm, less than or equal to about100 nm, less than or equal to about 90 nm, less than or equal to about80 nm, less than or equal to about 70 nm, less than or equal to about 60nm, less than or equal to about 50 nm, but is not limited thereto. Theelectron injection layer may be an organic layer formed by deposition.The electron transport layer may include an inorganic oxide or (nano orfine) inorganic oxide particles or may include an organic layer formedby deposition.

The quantum dot emission layer may be disposed in the hole injection (ortransport) layer or an electron injection (or transport) layer. Thequantum dot emission layer may be disposed as a separate layer betweenthe hole auxiliary layer and the electron auxiliary layer.

The charge auxiliary layer, the electron blocking layer, and the holeblocking layer may include, for example, an organic material, aninorganic material, or an organic/inorganic material. The organicmaterial may be a compound having hole or electron-related properties.The inorganic material may be, for example, a metal oxide such asmolybdenum oxide, tungsten oxide, zinc oxide, or nickel oxide, but isnot limited thereto.

The hole transport layer (HTL) and/or the hole injection layer mayinclude, for example, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS),poly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)-diphenylamine) (TFB), apolyarylamine, poly(N-vinylcarbazole) (PVK), polyaniline, polypyrrole,N,N,N′,N′-tetrakis (4-methoxyphenyl)-benzidine (TPD),4,4′,-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (α-NPD), m-MTDATA(4,4′,4″-tris[phenyl(m-tolyl)amino]triphenylamine),4,4′,4″-tris(N-carbazolyl)-triphenylamine (TCTA),1,1-bis[(di-4-tolylamino)phenylcyclohexane (TAPC), a p-type metal oxide(e.g., NiO, WO₃, MoO₃, etc.), a carbonaceous material such as grapheneoxide, or a combination thereof, but is not limited thereto.

The electron blocking layer (EBL) may include, for example,poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS),poly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)-diphenylamine) (TFB)polyarylamine, poly(N-vinylcarbazole), polyaniline, polypyrrole,N,N,N′,N′-tetrakis(4-methoxyphenyl)-benzidine (TPD),4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (α-NPD), m-MTDATA,4,4′,4″-tris(N-carbazolyl)-triphenylamine (TCTA), or a combinationthereof, but is not limited thereto.

The electron transport layer (ETL) and/or the electron injection layermay include, for example, 1,4,5,8-naphthalene-tetracarboxylicdianhydride (NTCDA), bathocuproine (BCP),tris[3-(3-pyridyl)-mesityl]borane (3TPYMB), LiF, Alq₃, Gaq₃, Inq₃, Znq₂,Zn(BTZ)₂, BeBq₂, ET204(8-(4-(4,6-di(naphthalen-2-yl)-1,3,5-triazin-2-yl)phenyl)quinolone),8-hydroxyquinolinato lithium (Liq), an n-type metal oxide (e.g., a zincoxide, HfO₂, etc.),8-(4-(4,6-di(naphthalen-2-yl)-1,3,5-triazin-2-yl)phenyl)quinolone:8-hydroxyquinolinatolithium (ET204:Liq),2,2′,2″-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) ora combination thereof, but is not limited thereto. In the foregoing “q”is 8-hydroxyquinoline, “BTZ” is 2-(2-hydroxyphenyl)benzothiazolate, and“Bq” is 10-hydroxybenzo[h]quinoline.

The hole blocking layer (HBL) may include, for example,1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA), bathocuproine(BCP), tris[3-(3-pyridyl)-mesityl] borane (3TPYMB), LiF, Alq₃, Gaq₃,Inq₃, Znq₂, Zn(BTZ)₂, BeBq₂, or a combination thereof, but is notlimited thereto.

In a device according to an embodiment, an anode 10 disposed on atransparent substrate 100 may include a metal oxide transparentelectrode (e.g., ITO electrode) and a cathode 50 facing the anode mayinclude a metal (Mg, Al, etc.) of a predetermined (e.g., relatively low)work function. TFB and/or PVK, for example, as a hole transport layer 20and PEDOT:PSS and/or a p-type metal oxide, for example, as a holeinjection layer 20 may be disposed between the transparent electrode 10and the emission layer 30. An electron auxiliary layer (e.g., electrontransport layer) 40 may be disposed between the quantum dot emissionlayer 30 and the cathode 50. (see FIG. 3)

A device according to an embodiment has an inverted structure. Herein, acathode 50 disposed on a transparent substrate 100 may include a metaloxide transparent electrode (e.g., ITO) and an anode 10 facing thecathode may include a metal (e.g., Au, Ag, etc.) of a predetermined(e.g., relatively high) work function. For example, an n-type metaloxide (ZnO) may be disposed between the transparent electrode 50 and theemission layer 30 as an electron auxiliary layer (e.g., an electrontransport layer) 40. A hole auxiliary layer 20 (e.g., a hole transportlayer including TFB and/or PVK and/or a hole injection layer includingMoO₃ or another p-type metal oxide) may be disposed between the metalanode 10 and the quantum dot emission layer 30. (see FIG. 4)

Hereinafter, specific examples are illustrated. However, these examplesare exemplary, and the present disclosure is not limited thereto.

EXAMPLES

Analysis Method

1. Photoluminescence Analysis

A photoluminescence (PL) spectrum of the produced nanocrystals areobtained using a Hitachi F-7000 spectrometer at an irradiationwavelength of 372 nanometers (nm).

2. Ultraviolet (UV) Spectroscopy Analysis

UV spectroscopy analysis is performed using a Hitachi U-3310spectrometer to obtain a UV-Visible absorption spectrum.

3. Inductively Coupled Plasma (ICP) Analysis

An inductively coupled plasma-atomic emission spectroscopy (ICP-AES)analysis is performed using Shimadzu ICPS-8100.

4. Transmission Electron Microscopy (TEM) Analysis

Transmission electron microscopy photographs of nanocrystals areobtained using an UT F30 Tecnai electron microscope.

5. Electroluminescence Analysis

When a voltage is applied, a current depending on the voltage ismeasured by using a current-voltage (IV) tester 2635B manufactured byKeithley Co., Ltd. and using CS-2000A of Konica Minolta Co., Ltd., anelectroluminescent brightness is measured.

Synthesis is performed under an inert gas atmosphere (nitrogen flowingcondition) unless particularly mentioned. In the following examples orthe like, a (amount) ratio between (or among) the precursors refers to amolar ratio unless defined to the contrary.

Synthesis of Quantum Dot Having a ZnTeSe Core and a ZnSe/ZnS ShellExample 1

Selenium, sulfur, and tellurium are dispersed in trioctylphosphine (TOP)to obtain a 2 molar (M) Se/TOP stock solution, a 2 M S/TOP stocksolution and a 0.1 M Te/TOP stock solution.

1. In a 300 milliliters (mL) reaction flask, zinc acetate is dissolvedin trioctyl amine together with palmitic acid, and is heated undervacuum at 120° C. In one hour, an atmosphere in the reactor is convertedinto nitrogen.

After being heated at 300° C., the prepared Se/TOP stock solution andTe/TOP stock solution are rapidly added in a predetermined ratio. After60 minutes, a reaction solution is rapidly cooled to room temperatureand acetone is added thereto to obtain precipitates, which are separatedvia centrifugation. The obtained ZnSeTe cores are dispersed in toluene.

The ratio between the used Zn precursors and the used Se precursors(Zn:Se) is 2:1 and a ratio between the amount of Te and the amount of Seis 0.03:1 (Te:Se).

2. In a 300 mL reaction flask, trioctylamine is placed and zinc acetateand oleic acid are added thereto at a ratio of 2:1 and placed undervacuum at 120° C. The atmosphere inside the flask is replaced withnitrogen (N₂). While a temperature of the reaction flask is increased to300° C., a toluene dispersion of the prepared ZnTeSe core is injectedrapidly and then Se/TOP stock solution is added thereto and a reactionproceeds for 120 minutes to form a ZnSe layer on the core. Then, a S/TOPis added together with zinc acetate and a reaction proceeds for 120 minto form a ZnS layer on the ZnSe layer. A ratio between the amounts ofthe Zn precursor, the S precursor, and the Se precursor is about3.5:2.5:1.

With respect to the quantum dots as prepared, an inductively coupledplasma atomic emission spectroscopic analysis is made and the resultsare summarized in Table 1.

With respect to the quantum dots as prepared, a photoluminescentanalysis is made and the results are summarized in Table 2.

Example 2

A core-shell quantum dot is prepared in the same manner as Example 1except that during the formation of the core, the ratio between theamounts of the Zn precursor and the Se precursor is 2:1, the ratio ofthe amounts of the Te precursor to the Se precursor (Te:Se) is 0.03:1,and, during the formation of the shell, a ratio between the amounts ofthe Zn precursor, the S precursor, and the Se precursor is about3.8:2.8:1

With respect to the quantum dots as prepared, an inductively coupledplasma atomic emission spectroscopic analysis is made and the resultsare summarized in Table 1.

With respect to the quantum dots as prepared, a photoluminescentanalysis is made and the results are summarized in Table 2.

With respect to the quantum dots as prepared, a transmission electronmicroscopic analysis is made. The results confirm that an averageparticle size of the quantum dots is about 12.3 nm.

Example 3

A core-shell quantum dot is prepared in the same manner as Example 1except that during the formation of the core, the ratio between theamounts of the Zn precursor and the Se precursor is 2:1, the ratio ofthe amounts of the Te precursor to the Se precursor (Te:Se) is 0.03:1,and, during the formation of the shell, a ratio between the amounts ofthe Zn precursor, the S precursor, and the Se precursor is about4.6:3.6:1

With respect to the quantum dots as prepared, an inductively coupledplasma atomic emission spectroscopic analysis is made and the resultsare summarized in Table 1.

With respect to the quantum dots as prepared, a photoluminescentanalysis is made and the results are summarized in Table 2.

Example 4

A core-shell quantum dot is prepared in the same manner as Example 1except that during the formation of the core, the ratio between theamounts of the Zn precursor and the Se precursor is 2:1, the ratio ofthe amounts of the Te precursor to the Se precursor (Te:Se) is 0.03:1,and, during the formation of the shell, a ratio between the amounts ofthe Zn precursor, the S precursor, and the Se precursor is about 3:2:1.

With respect to the quantum dots as prepared, an inductively coupledplasma atomic emission spectroscopic analysis is made and the resultsare summarized in Table 1.

With respect to the quantum dots as prepared, a photoluminescentanalysis is made and the results are summarized in Table 2.

With respect to the quantum dots as prepared, a transmission electronmicroscopic analysis is made. The results confirm that an averageparticle size of the quantum dots is about 7.8 nm.

Example 5

A core-shell quantum dot is prepared in the same manner as Example 1except that during the formation of the core, the ratio between theamounts of the Zn precursor and the Se precursor is 2:1, the ratio ofthe amounts of the Te precursor to the Se precursor (Te:Se) is 0.03:1,and, during the formation of the shell, a ratio between the amounts ofthe Zn precursor, the S precursor, and the Se precursor is about3.4:2.4:1

With respect to the quantum dots as prepared, an inductively coupledplasma atomic emission spectroscopic analysis is made and the resultsare summarized in Table 1.

With respect to the quantum dots as prepared, a photoluminescentanalysis is made and the results are summarized in Table 2.

TABLE 1 Mole ratio, X:Zn Mole ratio, Mole ratio, X = S X = Zn X = Se X =Te (Se + S):Zn S:Se Example 4 0.43:1 1.00:1 0.46:1 0.002:1 0.89:1 0.94:1Example 5 0.51:1 1.00:1 0.43:1 0.002:1 0.94:1 1.19:1 Example 1 0.51:11.00:1 0.41:1 0.002:1 0.92:1 1.24:1 Example 2 0.58:1 1.00:1 0.41:10.002:1 0.99:1 1.41:1 Example 3 0.56:1 1.00:1 0.31:1 0.002:1 0.88:11.81:1

TABLE 2 Full Width at Half Quantum Maximum Yield Mole PL (FWHM) (QY)ratio, (nm) (nm) (%) S:Se Example 4 445 30 72 0.94:1 Example 5 450 25 711.19:1 Example 1 450 29 85 1.24:1 Example 2 447 18 84 1.41:1 Example 3448 21 75 1.81:1

The results of Table 1 and Table 2 confirm that the quantum dots ofExamples may emit blue light with enhanced quantum efficiency andreduced FWHM.

Example 6

A core-shell quantum dot is prepared in the same manner as Example 1except that during the formation of the quantum dot, the ratios of theprecursors are controlled such that in a quantum dot thus prepared, theratio of sulfur with respect to selenium is 0.78:1.

Comparative Example 1

A core-shell quantum dot is prepared in the same manner as Example 1except that during the formation of the quantum dot, the ratios of theprecursors are controlled such that in the quantum dot thus prepared,the ratio of sulfur with respect to selenium is 2.67:1

Example 7

A light emitting device is fabricated by using the quantum dot ofExample 1 in the following manner. On a glass substrate with an ITOelectrode (anode) as deposited, apoly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)layer and a poly(N-vinylcarbazole (PVK) layer is formed via a spincoating method as a hole injection layer and a hole transporting layer,respectively. Over the PVK layer thus formed, an octane dispersion ofthe quantum dots are spin-coated to form a quantum dot emission layer,and over the quantum dot emissive layer, a2,2′,2″-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi)layer is formed as an electron auxiliary layer, over which an aluminumelectrode is vapor deposited.

For the prepared device, electroluminescent properties are evaluated andthe results are summarized in Table 3.

Example 8

An electroluminescent device is prepared in the same manner as set forthin Example 7 except for using the quantum dots of Example 2 as thequantum dot. For the prepared device, electroluminescent properties areevaluated and the results are summarized in Table 3.

Example 9

An electroluminescent device is prepared in the same manner as set forthin Example 7 except for using the quantum dots of Example 6 as thequantum dot. For the prepared device, electroluminescent properties areevaluated and the results are summarized in Table 3.

Comparative Example 2

An electroluminescent device is prepared in the same manner as set forthin Example 7 except for using the quantum dots of Comparative Example 1as the quantum dot. For the prepared device, electroluminescentproperties are evaluated and the results are summarized in Table 3.

TABLE 3 Candelas per square meter Maximum (Cd/m²) at 5 EQE milliamperesλ_(max)* FWHM (%) (mA) (nm) (nm) Example 7 6.3 134.1 452 33 Example 86.5 133.5 452 29 Example 9 6.8 145 452 19 Comp. Example 2 2.4 55 446 21*λ_(max): peak emission wavelength

The results of Table 3 confirm that the devices including the quantumdots of Examples may exhibit significantly improved electroluminescentproperties in comparison with the device including the quantum dots ofComparative Example.

While this disclosure has been described in connection with what ispresently considered to be practical example embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A quantum dot comprising: a semiconductornanocrystal comprising zinc, selenium, and sulfur, wherein the quantumdot further comprises tellurium, wherein the quantum dot does notcomprise cadmium, and in the quantum dot, a mole ratio of sulfur withrespect to selenium is less than or equal to about 2.4:1, wherein amaximum photoluminescent peak wavelength of the quantum dot is greaterthan or equal to about 430 nanometers and less than or equal to about480 nanometers, and wherein in the quantum dot, a mole ratio oftellurium with respect to selenium is less than or equal to about0.02:1.
 2. The quantum dot of claim 1, wherein the quantum dot does notcomprise an indium phosphide.
 3. The quantum dot of claim 1, wherein thequantum dot has a size of greater than or equal to about 10 nanometers.4. The quantum dot of claim 1, wherein in the quantum dot, a mole ratioof tellurium with respect to selenium is less than 0.01:1.
 5. Thequantum dot of claim 1, wherein in the quantum dot, the mole ratio ofsulfur with respect to selenium is less than or equal to about 2.0:1 anda mole ratio of tellurium with respect to selenium is in a range ofgreater than or equal to about 0.001:1 and less than or equal to about0.01.
 6. The quantum dot of claim 1, wherein in the quantum dot, themole ratio of sulfur with respect to selenium is less than or equal toabout 1.85:1.
 7. The quantum dot of claim 1, wherein a maximumphotoluminescent peak wavelength of the quantum dot is greater thanabout 440 nanometers and a maximum photoluminescent peak of the quantumdot has a full width at half maximum is less than or equal to 39 nm. 8.The quantum dot of claim 1, wherein the quantum dot has a core shellstructure wherein a core comprising a first semiconductor nanocrystalmaterial comprising zinc, tellurium, and selenium and a semiconductornanocrystal shell disposed on the core and comprising a secondsemiconductor nanocrystal comprising zinc, selenium, and sulfur.
 9. Thequantum dot of claim 1, wherein in the quantum dot, a mole ratio oftellurium with respect to zinc is less than 0.01:1.
 10. The quantum dotof claim 1, wherein in the quantum dot, a mole ratio of sulfur withrespect to zinc is greater than or equal to about 0.1:1.
 11. The quantumdot of claim 1, wherein in the quantum dot, a mole ratio of a sum ofselenium and sulfur with respect to zinc is greater than or equal toabout 0.3:1.
 12. The quantum dot of claim 1, wherein a maximumphotoluminescent peak wavelength of the quantum dot is greater than orequal to about 445 nanometers.
 13. The quantum dot of claim 1, whereinthe quantum dot has quantum efficiency of greater than or equal to about70%.
 14. The quantum dot of claim 1, wherein a full width at halfmaximum of a maximum photoluminescent peak of the quantum dot is lessthan or equal to about 30 nanometers.
 15. The quantum dot of claim 1,wherein the quantum dot has a size of greater than or equal to about 12nanometers.
 16. An electroluminescent device comprising a firstelectrode and a second electrode facing each other, and a light emittinglayer disposed between the first electrode and the second electrode,wherein the light emitting layer comprises a plurality of quantum dotsand the plurality of quantum dots comprises the quantum dot of claim 1.17. The electroluminescent device of claim 16, further comprising acharge auxiliary layer between the first electrode and the lightemitting layer, between the second electrode and the light emittinglayer, or between the first electrode and the light emitting layer andbetween the second electrode and the light emitting layer.
 18. Theelectroluminescent device of claim 17, wherein the charge auxiliarylayer comprises a charge injection layer, a charge transport layer, or acombination thereof.
 19. The electroluminescent device of claim 16,wherein a peak external quantum efficiency of the electroluminescentdevice is greater than or equal to about 4%.
 20. The electroluminescentdevice of claim 16, wherein the electroluminescent device emits lighthaving an x value of a CIE color space chromaticity diagram that is lessthan or equal to about 0.2.